Fluorescence is a characteristic of ________
A) dark nebulae
B) planetary nebulae
C) emission nebulae
D) blue nebulae
E) reflection nebulae
C
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Tropical forests are being deforested mostly as a result of
A. sustainable small-scale farming and raising of cash crops. B. cattle ranching and commercial logging. C. CITES. D. ecotourism. E. capital to pay off governmental debt.
On average, the water equivalent of 25.4 cm of snow is about how many centimetres of water?
A. 6.35 cm B. 5.08 cm C. 2.54 cm D. 1.27 cm
A main difference between gravitational and electric forces is that electrical forces
A) attract. B) repel or attract. C) obey the inverse-square law. D) act over shorter distances. E) are weaker.
Tides are principally caused by
A) friction. B) Earth's revolution of the Sun. C) gravity. D) velocity.